This invention generally relates to fluid flow control devices and more particularly to a controllable vortex generator for use on surfaces over which a fluid may flow such as the wing surfaces of an aircraft.
It is well known to attach an array of vortex generators to an aerodynamic surface of an aircraft to energize the downstream boundary layer and thereby reduce the tendency of airflow to separate from the surface under adverse pressure conditions. Flow separation on the upper surface of the wings of an aircraft is particularly undesirable in that it may result in the loss of lift and control. As a general rule, these problems arise only when the aircraft is operating at relatively slow speeds and at high angles of attack such as during approach and takeoff. During cruising flight, vortex generators are generally unnecessary and simply create additional drag.
Previous attempts have been made to minimize or eliminate the unnecessary drag produced by fixed-vane type vortex generators during cruising flight. For example, U.S. Pat. No. 5,253,828 discloses an array of vortex generators which are mounted to the leading edge of a wing flap. When the flap is retracted, the vortex generators are retracted within a panel covering the gap between the wing and the flaps. When the flap is deflected, the vortex generators are extended through slots in the panel into the airstream. Also, U.S. Pat. No. 4,039,161 discloses a somewhat similar invention in which pairs of opposing vortex generators are mounted within a wing structure just beneath the upper and lower surfaces, respectively, of the wing skin. The vortex generators, which are biased toward retracted positions by a pair of springs, are mechanically interconnected with an associated flap. When the flap is deflected upward, the lower vortex generator is extended downward into the air stream, and vice versa.
While both of these systems may be effective in reducing the cruise drag penalty associated with vortex generators, they have certain inherent disadvantages. First, because they introduce additional mechanical components into the aircraft, they inherently increase weight, as well as manufacturing and maintenance costs which may not be offset by the resulting fuel savings. Secondly, they might under some circumstances give rise to safety of flight problems. A failure in their mechanical systems could result in loss of lift or control under critical flight conditions and could interfere with operation of the associated control surfaces.
Accordingly, it is an object of this invention to provide for a controllable vortex generator which can be selectively moved between a deflected position where it will produce downstream turbulence and an undeflected position where associated drag will be minimized.
It is another object of this invention to produce such a vortex generator which can be manufactured and installed on an aircraft at a cost comparable to that of a conventional fixed-vane type vortex generator.
It is a further object of this invention to provide for a controllable vortex generator which is electrically operated and which would, upon failure of any part of the associated electrical system, return to the deflected system so as to eliminate any safety of flight problem.
This invention can be broadly summarized as providing for a controllable vortex generator which includes a fin and means for mounting the fin to a surface over which a fluid may flow such as the surface of an airplane wing. At least a portion of the fin is formed of a shape memory alloy and the invention also includes means for heating that portion.
According to a more detailed aspect of the invention, the fin includes a forward portion fixed with respect to the surface and an aft portion which is movable with respect to the forward portion.
According to another detailed aspect of the invention, the shape memory alloy consists essentially of nickel and titanium.
According to a yet more detailed aspect of the invention, the heating means includes an electrical resistance heating element mounted on the fin.
The invention can also be summarized as providing for a controllable vortex generator having deflected and undeflected positions. The vortex generator includes a fin, a portion of which is formed of a shape memory alloy, means for heating that portion, and means for mounting the fin to a surface over which a fluid may flow. It further includes means attached to the fin for biasing it toward the deflected position.
According to a more detailed aspect of the invention, the means for biasing is a spring. According to a yet more detailed aspect of the invention, the means for biasing is a leaf spring slidably mounted to the fin.